1. Field of the Invention
This invention relates primarily to food processing equipment, and, more particularly, to a continuous flow system for controlling the moisture content and sulphur dioxide concentration of food products and more specifically fruits and vegetable products.
2. Description of the Prior Art
Existing processes for controlling and equalizing the moisture content and/or sulphur dioxide concentration of dehydrated apple products are "batch" processes in which discrete quantities of product such as apples, are sequentially processed as a unit. A batch of product in range from 2,000 to 12,000 pounds is initially dried to a moisture content that is lower than the accepted market level which is greater than 14 to 16% but usually about 23%. This overdrying is necessary since fluxuations in moisture content cannot be allowed to exceed the accepted market level or target value since there are no provisions in conventional equalization processes for accurately reducing the moisture content to a specific value. At the same time, the concentration of sulphur dioxide in the product is reduced below the target value. After drying, the batch of product is stored in stationary piles or large revolving drums, and the batches are allowed to sit with or without agitation for a period of time usually between 8 and 48 hours. This storage period allows moisture within the batch to migrate from high to low levels until an overall equilibrium is reached. It is this migration process that is conventionally referred to as "equalizing". After the moisture content and sulphur dioxide concentration of the batch has been equalized, the moisture content of the batch is raised to the target value by the addition of water. This is accomplished by spraying water onto stationary piles of product. An additional equalizing step is sometimes used after the moisture content of the product has been raised. Either shortly before or directly after the moisture content of the product has been adjusted to the target value, the sulphur dioxide concentration is also adjusted in a batch process. This is usually accomplished by the injection of gaseous sulphur dioxide, with or without tumbling, or by placing the product in a chamber in the presence of burning rock sulphur. The product may then be allowed to further equalize for a period of time before being packaged for shipment. In summary, conventional processing techniques first batch dry the product below the target value, and then batch moisturize the product to the target value.
The principal disadvantages of a batch type process are its long process time and high cost. Batch processing systems do not lend themselves to automation so that product measurements and subsequent manipulation must generally be manually accomplished. Furthermore, the processing times for such batch type processes frequently run to as long as 40 hours. Consequently, the capital costs for processing high volumes of products is exceedingly large. Additionally, batch type re-drying processes require high unit costs and they are often detrimental to product quality.